A vault 2 is a huge ovoid bioparticle having a particle size of 40 nm×40 nm×67 nm, and it is a nucleic acid-protein complex having a largest molecular weight within a cell (see FIG. 2). Vault 2 present in an organism is constituted of three types of proteins (major vault protein (MVP), vault poly(ADP-ribose)polymerase (VPARP), and telomerase-associated protein-1 (TEP1)) and one type of RNA. Vault 2 is such that 39 MVPs 3, which are main components and have a molecular weight of approximately 100 kDa, gather to form a half vault in a shape of a bowl (each site being referred to as a cap 5, a shoulder 6, a body 7, and a waist 8) and two halves are associated at waist 8 as if edges of the bowls were coupled, to thereby form an outer shell of the ovoid particle. Components other than the MVP are present in an internal space formed by the outer shell.
MVP 3 forming the outer shell of vault 2 is constituted of 12 domains in total including 9 repeating structures (3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i) formed from antiparallel β sheets and shoulder 6, a cap helix 9, and a cap ring 10 (FIG. 3), and intermolecular hydrophobic bond between domains of cap helix 9 is important for formation of a half vault in a bowl shape. Two half vaults form the ovoid vault particle by associating N terminals of MVPs 3, and such association is formed only based on very weak interaction of ionic bond and a short intermolecular β sheet. Such structural information of the vault and a mechanism of formation of a particle have been clarified as the present inventor succeeded in overall structure determination of a rat liver derived vault in 2009 (see, for example, Hideaki Tanaka et al., “The Structure of Rat Liver Vault at 3.5 Angstrom Resolution,” Science, Vol. 323, pp. 384-388 (2009) (NPD 1)).
It has previously been known that as an MVP which is a main component of a vault is expressed in an insect cell, an ovoid particle the same as in an organism is formed (see, for example, Andrew G. Stephen et al., “Assembly of Vault-like Particles in Insect Cells Expressing Only the Major Vault Protein,” The Journal of Biological Chemistry, Vol. 276, No. 26, pp. 23217-23220 (2001) (NPD 2)). Owing to a characteristic shape of a vault, development of a drug delivery system (DDS) by using the vault as a nanocapsule has progressed (see, for example, Valerie A. Kickhoefer et al., “Engineering of vault nanocapsules with enzymatic and fluorescent properties,” PNAS, Vol. 102, No. 12, pp. 4348-4352 (2005) (NPD 3) and Valerie A. Kickhoefer et al., “Targeting Vault Nanoparticles to Specific Cell Surface Receptors,” ACS nano, 3 (1): 27-36.doi: 10.1021/nn800638x(2009) (NPD 4)).
For example, Japanese National Patent Publication No. 2013-509202 (PTD 1) has disclosed use of a vault particle which is a recombinant particle having an MVP as well as a fusion protein and mINT and a protein of interest (cytokine) for delivery of the protein of interest to a cell or a tumor, or a target. In addition, for example, Japanese National Patent Publication No. 2007-508846 (PTD 2) has disclosed a technique directed to a composition for delivering a polynucleotide packaged by a polypeptide, having a leucine zipper as a polynucleotide-bound domain.
In a conventional method, for taking a drug into a particle, a C terminal 160 residue (an INT domain: bonding to an MVP) of a VPARP which is a constituent component of a vault and present in a particle is used as a tag. Such use is also for having the particle retain the drug therein. This method, however, has not yet successfully made full use of a large internal space in the vault.